Machine tools of this type comprising two dimensionally rigid parallel side walls, a cross slide displaceable on guides on the top surface of the side walls and a front machining unit that can be equipped with chipping tools are referred to as so-called gantry machines. Usually, in this machine type the cross slide moving in the Y coordinate axis on parallel guide rails on the two side walls forms a crosshead and supports a longitudinal slide displaceable in the X coordinate axis. A vertical slide that can be displaced in the Z coordinate axis may be guided on this longitudinal slide as a carrier of a machining unit. Mostly, a workpiece table is used as workpiece mounting unit for one or more workpieces to be machined, which is mounted in the space between the two side walls on the machine bed.
In order to achieve multi-axis and multi-side machining options of a workpiece in one clamping, the workpiece table may be realized as a rotationally driven rotary table in more complex machines of this type. A dimensionally stable bed-like bottom connects the two side walls so that they form a dimensionally rigid overall construction having a favorable temperature or heat behavior. In conventional machines of this type the workpiece mounting unit is mounted to the bed-like bottom mostly in the shape of a rotary or swiveling table construction. One of the particular advantages of the gantry constructional style is the high rigidity of the machine frame which enables maximal machining precision as well as high static and dynamic loads and correspondingly high chipping performances. Furthermore, the symmetric structure of the machine frame has a favorable effect on the temperature behavior of the overall machine. However, a disadvantage of this machine type is a limited accessibility to the workpiece table for placing and removing workpieces. Access to the work area in conventional gantry-type machines is limited by the front parts of the two side walls so that loading and unloading always has to be done directly from the front.
Furthermore, machine tools are known, for example, from German patent, DE 10 2006 034 123 B4, whose machine frame has two side walls and a bottom-like bed solidly fixed to one another. A slide construction and a machining unit thereon are disposed on the side walls so as to be displaceable in three coordinate axes via linear guides. In order to achieve a five-axis machining option of a workpiece a swiveling bridge table is provided between the two side walls. The swiveling bridge is supported in two end-side stable support bearings in the side walls of the machine frame so that it can be swiveled about a horizontal transverse axis. For performing the swiveling movements, two electrically synchronized direct drives, preferably torque motors, are used. A rotary table that can rotate about a vertical central axis and serves to solidly accommodate a workpiece is disposed in the bridge part between the two support bearings. In this machine, the swiveling bridge of the swiveling bridge table is not directly supported in the two side walls of the machine frame but in two slides, these slides being synchronously displaceable on linear guides on the inner surfaces of the two side walls of the machine frame. As drive units two electrically synchronized linear motors are used whose electrically active components are disposed between the slides and the side walls. Due to the possibility to displace the swiveling bridge in the direction of the Y coordinate axis, accessibility to the workpiece table is improved which, however, is achieved only by accepting more technical effort due to, among others, the linear adjusting drives of the swiveling bridge construction. In addition thereto, the integration of powerful electric direct drives into the central bridge part of the swiveling bridge for obtaining a powerful direct drive of the rotary table causes problems because there is only a limited space for the electric motor. By accommodating the swiveling axis in the two support bearings in the side walls of the frame, it is possible to achieve sufficiently high rigidity even in case of large diameters of the tool tables. However, the high amount of material input and the relatively large space required for the swiveling bridge are a disadvantage. When the workpiece support is turned to the 90° position, a limitation of the work area may result and, as the case may be, reduce the rigidity of the overall construction.
In addition to the machine tools in gantry constructional style, complex machine tools and machining centers, respectively, for machining workpieces in multiple axes, particularly five axes, are known that have three linear axes disposed in a Cartesian manner as well as two rotational axes. The machining unit can be displaced by a motor on the top side on a machine frame in a horizontal plane in the X and Y axes via a compound slide and is mounted to the front of the table construction so as to be displaceable in the Z axis via a vertical slide. A machine tool of this type, known from German patent publication DE-A 196 41 831, has a circular recess in the vertical front wall thereof in which the circular foot of a support console is supported so that it can be rotated by a motor about a horizontal axis by using a suitable bearing structure. The circular disk-shaped console foot is a part of a projecting support console that has a support surface running parallel to the rotational axis in its free end area for supporting a rotary table. The rotary table provided with chucking grooves for fixing a workpiece may be directly driven by a suitable drive unit or via gearing means. Due to contradicting requirements for a dynamic interpolating machining the point of intersection of the two rotational axes is relatively far above the table surface. This means that when the workpiece table is turned to the vertical 90° position, a relatively large part of the work area is lost and relatively large linear movements of the machining unit have to be carried out in the XYZ coordinate system during five-axis machining. In addition thereto, a change of the bending of the projecting console part due to its own weight and the weight of the workpiece during the rotation about the horizontal swiveling axis may have a negative effect. As the direction of the force attack changes, different deformation conditions result.
Apart from that, a machine tool for machining workpieces in five axes is known from German patent publication DE 44 44 614 A, in which a recess having a support surface inclined by 45° is formed in the front of a continuous machine stand. On this support surface, inclined at an angle of 45° to the vertical, rests a circular or circular ring-shaped foot of a console which has a forward pointing support projection including a rotational axis aligned by 45° to the rotational axis of the console foot. A rotary table rotatable about a vertical axis is supported on this support surface, which contains chucking means for fixing a workpiece on the top surface thereof.
German patent publication DE 10 2004 049 525 A describes a similarly designed machine tool in which the console foot is not centrally disposed in a recess or on the face of the pedestal of the machine stand but is laterally offset relative to the center of the machine stand. The console is located in a corner area at the front of the machine stand and supported there in a pivoted manner on the surface inclined by 45° of a pedestal. This arrangement allows an over-tilted position of the rotary table and thus negative orientation angles relative to the vertical Z axis. This embodiment exhibits the special fact that when the workpiece table swivels therethrough, a corresponding recess must be provided in the machine bed, which impairs the arrangement and selection of powerful direct drives. For example, the direct drives required for turning large workpieces demand corresponding dimensions, in particular, sufficient overall heights.